MySQL Programming Interview Question:

How To Add a New Column to an Existing Table in MySQL?

Submitted by: Administrator

If you have an existing table with existing data rows, and want to add a new column to that table, you can use the "ALTER TABLE ... ADD COLUMN" statement. The tutorial script below shows you a good example:

mysql> ALTER TABLE tip ADD COLUMN author VARCHAR(40);
Query OK, 1 row affected (0.18 sec)
Records: 1 Duplicates: 0 Warnings: 0
<pre>mysql> SHOW COLUMNS FROM tip;
+-------------+--------------+------+-----+---------+-------
| Field | Type | Null | Key | Default | Extra
+-------------+--------------+------+-----+---------+-------
| id | int(11) | NO | PRI | |
| subject | varchar(80) | NO | | |
| description | varchar(256) | NO | | |
| create_date | date | YES | | NULL |
| author | varchar(40) | YES | | NULL |
+-------------+--------------+------+-----+---------+-------</pre>
5 rows in set (0.01 sec)

This SQL script added a new column called "author" to the "tip" table. NULL values were added to this column on all existing data rows.
Submitted by: Administrator